Method and apparatus for connecting a plurality of battery cells in series or parallel

ABSTRACT

Methods and systems for selectively connecting a plurality of battery cells in a dual-mode battery pack in series and parallel configurations and/or for individual cell monitoring. A dual-mode battery pack may generally include a housing; a first set of battery cells connected in series; and a second set of battery cells connected in series. The battery pack may also include series connection contacts selectively connectable to the first set of battery cells and to the second set of battery cells and, when engaged, connecting the first set of battery cells and the second set of battery cells in a series configuration; and parallel connection contacts selectively connectable to the first set of battery cells and the second set of battery cells and, when engaged, connecting the first set of battery cells and the second set of battery cells in a parallel configuration.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/415,232, filed May 17, 2019, now U.S. Pat. No. 10,892,624, whichclaim priority to U.S. patent application Ser. No. 15/376,497, filedDec. 12, 2016, which claims priority to U.S. Provisional PatentApplication No. 62/266,215, filed on Dec. 11, 2015, the entire contentsof which are hereby incorporated by reference.

FIELD

The present invention generally relates to battery packs and, morespecifically, to battery packs in power tools and other electricaldevices.

SUMMARY

Generally, within a particular platform, power tools and otherelectronic devices (generally referred to herein as “tools” or a “tool”)and the associated battery packs are configured to operate at aparticular voltage level (e.g., 12V, 18V or 28V). In some cases, it maybe desirable to operate a tool at a higher voltage than available from aparticular battery pack (e.g., 36V instead of 18V). While it is possibleto put more cells in series to make new higher voltage battery packs(e.g., 36V packs) for the higher voltage-capable tools, this wouldrequire the user to purchase separate higher voltage packs, which wouldnot be able to power tools at the lower voltage.

Accordingly, it may be advantageous for a user to be able to use anavailable battery pack to drive a tool at a lower voltage (and with anincreased amp-hour capacity or run-time) in some instances or, in otherinstances, to drive a tool at a higher voltage. This option allows theuser to use a single battery pack in each instance, rather than havingseparate low-voltage and high-voltage battery packs. Therefore, atechnique to change the voltage of a battery pack (e.g., with 10 cells)between a lower voltage and a higher voltage (e.g., 18V and 36V) may bedesirable to allow a single battery pack to selectively output differentvoltages depending on whether the battery pack is coupled to a deviceoperating at a low voltage or a high voltage (e.g., 18V and 36V).

Embodiments disclosed herein are generally made with reference to 18Vand 36V voltage levels for the parallel and series configurations,respectively. However, the embodiments and the disclosed techniques arenot limited to these particular voltage levels and are similarlyapplicable to different voltage levels (for example, 12V and 24V, 20Vand 40V, 28V and 56V, 60V and 120V, as well as other voltage levels),configurations, amp-hour capacities, etc.

Independent embodiments and methods may be provided to selectivelyconnect a plurality of battery cells in a dual-mode battery pack inseries and parallel configurations.

The dual-mode battery pack may be set to either the series or parallelconfiguration depending on the power tool or other electrical deviceattached to the pack. For example, when a tool operating at a lowervoltage (e.g., 18V) is coupled to the dual-mode battery pack, the packis set to a parallel configuration to output the lower voltage (whileproviding an increased amp-hour capacity or run-time); when a tooloperating at a higher voltage (e.g., 36V) is coupled to the dual-modebattery pack, the pack is set to a series configuration to output thehigher voltage. The low-voltage tool and the high-voltage tool may bedifferent devices or may be a device operating in different modes.

Several different battery pack and tool configurations may be used toimplement the dual-voltage capability. A tool may have a physicalconfiguration to, upon coupling with the battery pack, cause thedual-mode battery pack to automatically configure or be configured toone of the series or parallel arrangement to output the appropriatevoltage level for that tool. For example, an arrangement of insulatingribs, recesses, and contacts on the tool(s) and/or the dual-mode batterypack may result in such a configuration (see, e.g., FIGS. 15-23 ).

Additionally, in some constructions, a user actuator (e.g., a toggleswitch) may be provided on the battery pack to mechanically make andbreak electrical connections to switch between series and parallelconfigurations of the battery pack.

Further, in some constructions, solid-state electronics (e.g., in thetool and/or the battery pack) may switch between the series and parallelconfigurations either automatically (e.g., upon a monitoring circuitdetecting a characteristic of a tool being attached) or manually (e.g.,via a user selection (the toggle switch)).

In one independent embodiment, a dual-mode battery pack may generallyinclude a housing; a first set of battery cells connected in series andpositioned in the housing; a second set of battery cells connected inseries and positioned in the housing; series connection contactsselectively connectable to the first set of battery cells and to thesecond set of battery cells and, when engaged, connecting the first setof battery cells and the second set of battery cells in series; andparallel connection contacts selectively connectable to the first set ofbattery cells and the second set of battery cells and, when engaged,connecting the first set of battery cells and the second set of batterycells in parallel.

In another independent embodiment, a method may be provided forconfiguring a dual mode battery pack. The method may generally includedisengaging, with an insulating rib of a tool, parallel connectioncontacts operable to connect a first set of battery cells and a secondset of battery cells in parallel; and engaging, with conducting bladesof the tool, series connection contacts operable to connect the firstset of battery cells and the second set of battery cells in series.

In yet another independent embodiment, a dual-mode battery pack maygenerally include a housing; a first set of battery cells connected inseries and positioned in the housing; a second set of battery cellsconnected in series and positioned in the housing; a first analog frontend connected to the first set of battery cells and configured toindividually monitor the first set of battery cells; a second analogfront end connected to the second set of battery cells and configured toindividually monitor the second set of battery cells; and an electronicprocessor connected to the first analog front end and the second analogfront end.

Other independent aspects of the invention will become apparent byconsideration of the detailed description, claims and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a first configuration of battery cellsin a battery pack.

FIG. 2 is a schematic diagram of a second configuration of battery cellsin a battery pack.

FIG. 3 is a schematic diagram of a configuration of switches in abattery pack.

FIG. 4 is a schematic diagram of a configuration of switches in abattery pack.

FIG. 5 is a schematic diagram of a configuration of switches in abattery pack.

FIG. 6 is a circuit diagram of one construction of a battery pack.

FIG. 7 is a circuit diagram of an alternative construction of a batterypack.

FIG. 8 is a circuit diagram of another alternative construction of abattery pack.

FIG. 9 is a circuit diagram of yet another alternative construction of abattery pack.

FIG. 10 is a circuit diagram of a further alternative construction of abattery pack.

FIG. 11 is a circuit diagram of another alternative construction of abattery pack.

FIG. 12 is a circuit diagram of yet another alternative construction ofa battery pack.

FIG. 13 is a circuit diagram of a further alternative construction of abattery pack.

FIG. 14 is a circuit diagram of a PCB implementation of a battery pack.

FIG. 15 is a side view of a battery pack.

FIG. 16 is a partial cross-sectional side view of the top housing of thebattery pack of FIG. 15 .

FIG. 17 is a partial cross-sectional side view of a portion of the tophousing of the battery pack of FIG. 15 .

FIG. 18A is the bottom view of the top housing of the battery pack ofFIG. 15 .

FIG. 18B is an enlarged bottom view of a portion of the top housing asshown in FIG. 18A.

FIG. 19A is a rear view of the top housing of the battery pack of FIG.15 .

FIG. 19B is an enlarged rear view of a portion of the top housing asshown in FIG. 19A.

FIG. 20 is a bottom view of the top housing of the battery pack of FIG.15 , illustrating the mechanical contacts.

FIG. 21 is a bottom perspective view a top housing of a power tool.

FIG. 22 is a bottom perspective view of an exemplary configuringmechanism between the battery pack of FIG. 15 and the power tool of FIG.21 .

FIG. 23 is a bottom perspective view of another exemplary configuringmechanism between the battery pack of FIG. 15 and the power tool of FIG.21 .

FIG. 24 is a block diagram of a battery monitoring circuit of a batterypack.

FIG. 25 is a block diagram of a battery monitoring circuit of a batterypack in a parallel configuration.

FIG. 26 is a block diagram of the battery monitoring circuit of FIG. 25in a series configuration.

FIG. 27 is a block diagram of a battery monitoring circuit of a batterypack in a series configuration.

FIG. 28 is a block diagram of the battery monitoring circuit of FIG. 27in a parallel configuration.

FIGS. 29A-29C are views of a housing half of a tool, such as a highervoltage (36V) tool.

FIG. 30 is a block diagram of a battery monitoring circuit.

FIG. 31 is a block diagram of an alternative battery monitoring circuit.

FIG. 32 is a block diagram of a battery monitoring circuit using sharedinter-integrated circuit bus.

FIGS. 33A-33B are block diagrams of a battery monitoring circuit usingmultiplexors and a shared inter-integrated circuit bus.

FIG. 34 is a block diagram of a battery monitoring circuit usingmultiple inter-integrated circuit buses.

FIG. 35 is a block diagram of a battery monitoring circuit using aserial peripheral interface.

FIG. 36A-C are views of a housing half of a tool, such as a lowervoltage (18V) tool.

DETAILED DESCRIPTION

Before any independent embodiments of the invention are explained indetail, it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement ofcomponents set forth in the following description or illustrated in thefollowing drawings. The invention is capable of other independentembodiments and of being practiced or of being carried out in variousways.

Various techniques and configurations of the battery packs may be usedto switch the battery pack between a configuration providing a loweroutput voltage level (and with an increased amp-hour capacity orrun-time) and a configuration providing a higher output voltage level.FIGS. 1-2 illustrate, in a battery pack 40 for a tool 44 (see FIGS.15-23 ), two exemplary battery cell connection layouts 4, 16 (withoutswitches) for providing a series configuration, for a higher voltageoutput, and a parallel configuration, for a lower voltage output and anincreased amp-hour capacity or run-time. The first layout 4 (see FIG. 1) generally includes five blocks 8 in a series connection, with eachblock 8 having two cells 12 in parallel. The second layout 16 (see FIG.2 ) generally includes a block 20 of five series-connected cells 12 inparallel with another block 20 of five series-connected cells 12. Eachconfiguration provides the same nominal output voltage as well ascapacity.

As an example, each cell 12 may have a lithium-based chemistry and anominal voltage of about 3.6V with a capacitance of about 1500milliampere hours (mAh). Five such cells 12 connected in series providea total nominal output voltage of 18V, and ten such cells 12 connectedin series provide a total nominal output voltage of 36V. Other numbersof cells 12 and/or cell types (with different chemistries, voltagelevels, capacities, etc.) may be used in other embodiments to providedesired characteristics of the battery pack 40.

As described in detail below, an Analog Front End (AFE) or other circuitmay be used to monitor the cells 12. In the first layout 4, monitoringeach pair of cells 12 (i.e., each block 8) may be sufficient. In thesecond layout 16, each cell 12 may be monitored. Some embodiments mayfurther include cell balancing circuitry to balance cells 12 of thebattery pack 40 when in a parallel configuration.

To transition either configuration between a parallel configuration(with lower voltage output and a series configuration (with a highervoltage output), a switching mechanism may be employed. Several switchesmay be placed in the various circuits to switch between the parallel andseries configurations. Those switches may be realized using, forexample, mechanical switches, relay switches, bipolar junctiontransistors (BJTs), metal-oxide-semiconductor field-effect transistors(MOSFETs), etc.

In the first layout 4 (FIG. 1 ), one block 8 may use at least threeswitches 24 to switch between the parallel and series connection of thecells 12. FIG. 3 illustrates how the switches 24 may be arranged toswitch such a block 8 between the parallel and series configurations.Applying this approach to the circuit from FIG. 1 would result infifteen switches 24, as shown in FIG. 4 . In FIG. 5 , three switches 24are used in combination with the second layout 16 (FIG. 2 ) to implementa technique to switch between a series and parallel connection of theblocks 20 and the cells 12.

Several different switching techniques may be used to accomplishswitching between series and parallel configurations. Several suchapproaches are discussed below for illustration purposes. Otherapproaches, however, are also possible and contemplated by thisdisclosure.

FIG. 6 illustrates a circuit 28 for a dual-mode battery pack 40 forselectively connecting cells 12 in series and parallel configurationswith a configuring mechanism. As illustrated, the circuit 28 includestwo blocks 20 of five cells 12 (e.g., as in the second cell layout 16).Each block 20 of five cells 12 is connected to parallel contacts 32 andto series contacts 36. The cells 12 are connected by wires and throughthe selected contacts 32, 36 to a connection point (power contacts (notshown)) for electrically connecting to the tool.

When the user connects a tool 44 to the battery pack 40, this connectionmay be used to determine whether the battery pack 40 operates in theseries configuration of the battery cells 12 to provide high voltage orin the parallel configuration of the battery cells 12 to provide a lowvoltage. The cells 12 in the dual-mode battery pack 40 are connected inparallel when the configuring mechanism (e.g., on the tool 44) (1) opens(or leaves open) the series connection contacts 36 and (2) closes (orleaves closed) the parallel connection contacts 32. Alternatively, thecells 12 are connected in series when the configuring mechanism (1)opens (or leaves open) the parallel connection contacts 32 and (2)closes (leaves closed) the series connection contacts 36.

In FIG. 6 , the bars S1, P1, and P2 symbolize the tool 44, which isapproaching and which, under different circumstances, closes or opensthe contacts 32, 36 for the series or parallel configuration. When theP1 and P2 bars are conducting and the S1 bar is open, the cells 12 arein a parallel configuration. When S1 bar is conducting and the P1 and P2bars are open, the cells 12 are in a series configuration.

Alternatively, in some instances, one or more of the bars S1, P1, and P2that are not conductors are part of the tool 44. For example, theparallel connection contacts 32 may be normally-closed contacts of thebattery pack 40 that are electrically separated (e.g., by an insulatorof the tool 44) in the series configuration.

The series connection bar S1 may include a conducting blade contact of atool 44 that interfaces with normally-open series connection contacts 36of the battery pack 40. The normally-open series connection contacts 36are open in the parallel configuration and then closed (e.g., by theconducting bar S1 of the tool 44) in the series configuration.

For example, when a tool operating at a low voltage is coupled to thebattery pack 40, the parallel connection contacts 32 are undisturbed andleft in their normally-closed state, while the series connectioncontacts 36 are also undisturbed and left in the normally-open state, toprovide the low voltage, parallel configuration of the battery pack 40for powering the tool. When a tool operating at a high voltage iscoupled to the battery pack 40, insulating ribs (for example,represented by bars P1 and P2) of the tool separate and place theparallel connection contacts 32 in an open state, while a conductingblade (the bar S1) of the tool connects and places the series connectioncontacts 36 in a closed state, to provide the high voltage seriesconfiguration of the battery pack 40 for powering the tool.

FIGS. 15-23 illustrate a mechanism for configuring the circuit 28 ofFIG. 6 . More particularly, a connection between a dual-mode batterypack 40 and a power tool 44 is illustrated. The dual-mode battery pack40 has (see FIG. 20 ) two sets of contacts: parallel connection contacts48 and series connection contacts 52. The parallel connection contacts48, when closed, connect the cells 12 in a parallel configuration, andthe series connection contacts 52, when closed, connect the cells 12 ina series configuration. To avoid a short circuit, both the parallelconnection contacts 48 and the series connection contacts 52 may not beclosed at the same time.

The dual-mode battery pack 40 will be selectively and alternativelyconfigured in the parallel configuration or the series configurationdepending on the voltage level for operating the attached tool. Forexample, when a tool operating at a low voltage (e.g., 18V) is coupledto the pack 40, the pack 40 is set to the parallel configuration tooutput the low voltage level. When a tool operating at a high voltage(e.g., 36V) is coupled to the pack 40, the pack 40 is set to the seriesconfiguration to output the high voltage level.

To this end, with the normally-closed parallel contacts 48 and thenormally-open series contacts 52, the tool operating at the low voltagelevel is configured to avoid interfering with or changing the normalcondition of the contacts 48, 52. In contrast, the tool operating at thehigh voltage level interferes with and changes the normal condition ofthe contacts 48, 52

Specifically, the tool includes insulating structure (e.g., ribs 56 madefrom insulating material (e.g., plastic)) electrically separating theparallel connection contacts 48 and conducting structure (e.g., bladecontacts 60) electrically connecting the series connection contacts 52.The illustrated mechanism is constructed and arranged so that the ribs56 separate the parallel connection contacts 48 before the bladecontacts 60 close the series connection contacts 52. For example, FIGS.18A-18B illustrate the parallel connection contacts 48 being positionedforwardly of the series connection contacts 52 along an insertion axis64 so that the parallel connection contacts 48 are engaged before theseries connection contacts 52 would be engaged.

The illustrated configuring mechanism involves three insertion stages asthe dual-mode battery pack 40 is slid onto a tool operating at a highvoltage level:

Insertion stage 1 (pre-insertion)

-   -   The parallel connection contacts 48 are closed.    -   The series connection contacts 52 are open.

Insertion stage 2 (mid-insertion)

-   -   The parallel connection contacts 48 are opened.    -   The series connection contacts 52 remain open.

Insertion stage 3 (battery pack 40 is electrically coupled to the tool44)

-   -   The parallel connection contacts 48 remain open.    -   The series connection contacts 52 are closed.

Likewise, the illustrated configuring mechanism involves three removalstages as the dual-mode battery pack 40 is removed from the tooloperating at a high voltage level:

Removal stage 1 (pre-removal)

-   -   The parallel connection contacts 48 are open.    -   The series connection contacts 52 are closed.

Removal stage 2 (mid-removal; the battery pack 40 is electricallydisconnected from the tool 44)

-   -   The parallel connection contacts 48 remain open.    -   The series connection contacts 52 are opened.

Removal stage 3 (the battery pack 40 is removed from the tool 44)

-   -   Parallel connection contacts 48 are closed.    -   Series connection contacts 52 are open.

As noted in the preceding example, when a tool operating at a lowvoltage level is coupled to the dual-mode battery pack 40, the tool isconfigured to avoid interfering with or changing the normal condition ofthe contacts 48, 52 such that the pack 40 remains in a parallelconfiguration to output the low voltage level. To assist in doing so(see FIG. 20 ), the illustrated contacts 48, 52 (part of a switchingterminal block 76) are recessed below a top surface of the battery packhousing 68.

The battery pack 40 includes a power terminal block 72 on a top portionof the housing 68 with positive and negative terminals (not shown) forconnecting to the positive and negative terminal (not shown) of thepower tool 44. In the example with low voltage operation, the toolengages the power tool terminal block 72, but not the switching terminalblock 76.

In contrast, with high voltage operation, the tool engages both thepower terminal block 72 (to engage the power terminals of the batterypack 40) and the switching terminal block 76 (to switch the pack 40 tothe series configuration). Specifically, the configuring mechanismincludes projections on which the ribs 56 and blade contacts 60 aresupported to extend into the recessed portion below the top surface ofthe pack housing 60 to engage and change the condition of the contacts48, 52.

A rail system to guide a battery 40 onto a tool 44 may also be used forthe mechanical construction of the switching battery (e.g., forembodiments of FIG. 6-14 ). As shown in FIG. 15 , the contacts 48, 52are shifted vertically as well as horizontally. The parallel connectioncontacts 48 axially toward the front are engaged and opened before theseries connection contacts 52 toward the rear are closed. Furthermore,the vertical shift between the contacts 48, 52 allows for a gap for theconfiguring mechanism to be as narrow as possible. The contacts 48, 52are further illustrated in FIGS. 16-20 .

The illustrated contacts 48, 52 are mounted with perfboards. Theparallel connection contacts 48 in the front are pressed into thematerial which surrounds the parallel connection contacts 48 to ensurethat the parallel connection contacts 48 stay in position and maintain aspring tension. The parallel connection contacts 48 are opened by theinsulating ribs 56 and spring closed to re-establish the parallelconnection whenever the ribs 56 slide out to ensure an idle or defaultparallel configuration.

A tool 44 operable at a high voltage level is partially shown in FIG. 21. The illustrated portion (e.g., the bottom of the handle) is engageablewith the battery pack 40. As illustrated, the tool 44 includes a numberof insulating elements (e.g., two plastic or polymer ribs 56. A numberof conductors (e.g., two blade contacts 60) are provided rearwardly ofand below the ribs 56.

FIGS. 22-23 illustrate engagement of the ribs 56 and contacts 60 on thetool 44 with the contacts 48, 52 of the battery pack 40. As illustrated,the ribs 56 split and separate the parallel connection contacts 48 whilethe blade contacts 60 close the series connection contacts 52. Asdescribed above, the ribs 56 and the contacts 60 are arranged such thatthe ribs 56 open the parallel connection contacts 48 before the bladecontacts 52 close the series connection contacts 52.

FIGS. 29A-C illustrate a housing half 80 of a tool operating at a highvoltage level. The housing half 80 includes a bottom handle portion 84for receiving the battery 40. As shown, the handle portion 84 includesan insulating rib 56 for separating the normally-closed parallelconnection contacts 48. FIGS. 36A-36C illustrate a housing half 180 of atool operating at a low voltage level. The housing half 180 includes abattery handle portion 184 for receiving the battery 40. However, thehandle portion 84 does not include insulating ribs or conductive blades.

In other constructions (not shown), the parallel connection contacts 48and the series connection contacts 52 of the battery pack 40 are bothnormally open and in a non-connected state. When a tool operating at alow voltage is attached to the battery pack 40, blade contacts 60 of thetool close the parallel connection contacts 48, while the seriesconnection contacts 52 remain open. When a tool operating at a highvoltage is attached to the battery pack 40, blade contacts 60 of thetool close the series connection contacts 52, while the parallelconnection contacts 48 remain open. In each case, the tool may alsoinclude insulating structure (e.g., ribs 56) to engage and insulate thecontacts which will remain open (e.g., the series connection contacts 52in the parallel configuration and the parallel connection contacts 48 inthe series configuration).

FIG. 7 illustrates an alternative circuit 88 for selectively connectingcells 12 in the parallel and series configurations. A differentconfiguring mechanism between the tool 44 and the battery pack 40includes a number of switches (e.g., five switches 92, 94, 96, 98, and100) instead of the connection contacts 48, 52 of FIG. 6 . Compared toFIG. 6 , the number of contacts may be reduced to one or two contacts.

The switches 92, 94, 96, 98, and 100 may have switching times in thenanosecond range, and the pack 40 may be designed such that the firstcontact opens as soon as the pack 40 starts to engage the tool andcloses the second contact when the battery pack 40 and the tool arefully engaged. This arrangement will ensure that there is sufficienttime between the connections to prevent a short circuit.

A changeover device (e.g., a lever 104) on the pack 40, which may haveone contact actuated or triggered by the tool, may be used to implementswitching between series and parallel configurations. In the illustratedconstruction, the switches 92, 94, 96, and 98 for the parallelconfiguration are normally on based in a default position of thechangeover lever 104, and the switch 100 for the series connection isnormally off. As the lever 104 switches positions, the switches 92, 94,96, and 98 for the parallel connection are turned off, and, some timethereafter, the switch 100 for the series connection is turned on sothat the pack 40 is then switched to a series configuration.

Such a construction may accommodate, without any structural changes,existing tools operating at a low voltage (e.g., 18V tools) with theparallel configuration of the battery pack 40. Also, it may be possibleto drive the switches 92, 94, 96, 98, and 100 with low power.

Within a predefined state, a normally-closed contact may remain closedand drive the switches 92, 94, 96, and 98 for the parallelconfiguration. As a tool operating at a high voltage is engaged, thelever 104 may be triggered, for example, by sliding, by triggering asensor (e.g., a reed contact (not shown)), etc. The lever 104 switchesfrom the 1-3 connection to 1-2. The parallel circuit is opened, and,thereafter, the series circuit is closed. At this point, switches 92,94, 96, and 98 are off, and switch 100 will be driven by positive powersupply V+. The result is that the cells 12 are switched from the 5S2Pconfiguration to a series 10S1P configuration. The battery pack 40outputs the high voltage level, and the tool operates at that voltagelevel.

FIG. 8 illustrates another alternative circuit 108 for selectivelyconnecting cells 12 in the parallel and series configurations. Anelectronic processor 112 and a number of switches (e.g., three switches116, 118, 120, 122, and 124) are operable to configure the cells 12 inthe parallel and series configurations. In the illustrated embodiments,the lever 104 is replaced by the processor 112. Two standard input andoutput pins (standard I/O) may be used to drive the switches 116, 118,120, 122, and 124.

The circuit 108 operates in a manner similar to the circuit 88 of FIG. 7. The circuit 108 remains in a predefined state, in which the circuit108 is driven by the processor 112 in parallel to establish a lowvoltage configuration. As soon as tool operating at a high voltageengages the battery pack 40, an input of the processor 112 is triggeredto change the configuration of the circuit 108 to a series, high voltagelevel configuration.

During the predefined state, the switches 116, 118, 120, and 122 aredriven by the processor 112. As soon as the input at Pin 30 istriggered, the processor 112 can set Pin 10 to low and Pin 9 to high, todrive the switch 124 for the series circuit configuration. Programmingof the processor 112 allows desired timing of the opening of theswitches 116, 118, 120, and 122 before closing of the switch 124.

This system allows a dynamic solution, for example, if the tool (orother electrical device) is operable at both the low voltage level andthe high voltage level (e.g., if a motor of the tool is able to operateat both the low voltage level (e.g., 18V) as well as at the high voltagelevel (e.g., 36V)). Efficiency and/or operation of the tool may beimproved by selecting (e.g., automatically based on operationalcharacteristics, manually based on user input, etc.) the optimal ordesired operating voltage level.

In some constructions, Pin 30 of the processor 112 may be set to highand may be used as a user input (e.g., a user driven switch (notshown)). When a motor of the tool 44 or the load of another electricaldevice can operate under both the low voltage level and the high voltagelevel, the user driven switch may be used to select the series orparallel configuration.

In some constructions, an input of the processor 112 may also be drivenby a tool sensor (e.g., a reed contact (not shown)). The circuit 108with the processor 112 may remain in parallel, low voltage configurationas long as the reed contact input of the processor 112 is not triggered.An activator for the tool sensor (e.g., a magnet for the reed sensor)may be provided for the tool operating at a high voltage. When the tool44 approaches or engages the pack 40, the magnet may trigger the reedcontact to cause the processor 112 to configure the cells 12 from theparallel, low voltage configuration to the series, high voltageconfiguration. It should be understood that a similar sensor/activator(e.g., reed contact and magnet) may be used as the lever 104 in thecircuit 88 of FIG. 7 .

In some constructions, a transponder/near field communication (NFC)system may trigger an input of the processor 112 in the battery pack 40to configure the cells 12 between the parallel and seriesconfigurations. Typical NFC tags contain data between 48 bytes and 8kilobytes (kB), which may establish a unique manufacturer specifictechnique to clearly identify a tool operating at a high voltage level.

In some constructions, the tool sensor or the transponder/NFC approachmay be used in conjunction with the user selection approach. A userinput may be ignored if the processor 112 determines from a tool sensortransponder that the tool is not operating at or capable of operating athigh voltage level in a series configuration of the battery pack 40. Inyet other embodiments, the user input may also be used to override datafrom the tool sensor/transponder.

In some constructions, the tool 44 may direct configuration of the cells12 between the parallel and series configurations. The tool 44 mayinclude a data connection to the battery pack 40 to control the switches116, 118, 120, 122, and 124 in the battery pack 40. The tool 44 maytransmit information regarding the optimal configuration of the cells 12based on the construction of the tool (e.g., a motor capable ofoperating only in one of the parallel and series configurations), thecurrent or desired operational conditions of the tool (e.g., a highvoltage requirement, a desired increased run-time/capacity, etc.), etc.The battery pack 40 may then, based on the information received from thetool 44, reconfigure the connection of the cells 12 between the paralleland series configurations.

In some constructions, separate sensors may trigger selection of theparallel configuration and of the series configuration. For example, asensor (e.g., a Hall effect sensor) may be used in one component (i.e.,the tool 44 or the battery pack 40) to detect the presence or absence ofa sensed element (e.g., a magnet) in the other component. Detection ofthe magnet causes configuration of the battery pack 40 in one of theseries or parallel configurations, and determination of the absence ofthe magnet causes configuration of the battery pack 40 in the other ofthe series or parallel configuration.

In another example, one or more sensors (e.g., Hall effect sensors) inone component may detect the location or orientation (rather than merelythe presence) of one or more sensed elements (e.g., magnets) in theother component to determine whether to configure the battery pack 40 inthe series or parallel configuration.

Other sensors (e.g., mechanical, optical, electrical, magnetic,inductive sensors, etc.) may also be used to trigger configuration ofthe cells 12 in the series or parallel configurations. The output of theapplicable sensor(s) is provided to the processor 112, which configuresthe battery pack 40 in the series or parallel configuration.

FIG. 9 illustrates yet another alternative circuit 128 for selectivelyconnecting cells 12 in the series and parallel configurations. Acombination of digital gates (for example, AND gates and inverters) maybe used to switch the circuit 128 between series and parallelconnection. Within the idle state the parallel circuit is connected andas soon as a contact (in this case, a switch 132) is closed, the circuitswitches from the parallel connection to the series connection. In someembodiments, switches 136 and 140 with resistors R2 and R3 may be usedto determine whether the parallel or series circuit is completelyswitched off to prevent a short circuit.

In the illustrated embodiment, an AND gate 144 may be activated withhelp of inverters 148 and 152. When the AND gate 144 is activated,switches 156, 158, 160, and 162 are turned ON, and the battery pack 40is in a parallel configuration. Further, the AND gate 144 may alsoactivate an active delay circuit driven by switch 136. The active delaycircuit over switch 136 may be used to prevent an AND gate 164 fromturning ON.

When the switch 132 is triggered, the inverter 152 changes from high tolow, and an output of the AND gate 144 is switched OFF. At the samemoment, the AND gate 164 gets two high signals, but the AND gate 164 maynot be turned ON before the switch 136 is turned off. At this point, thecircuit 128 swaps the active and inactive lines, and the output of theinverter 148 changes from high to low, which may be used to prevent theAND gate 144 from turning ON. In this embodiment, five switches 156,158, 160, 162, and 168 provide a trigger sequence that closes the switch132 and may be used to switch between series and parallelconfigurations. The trigger may operate with a single contact, such asthe sensor, the reed contact or the transponder/NFC system, describedabove.

In the examples of FIGS. 7-9 , the switches 92, 94, 96, 98, 100, 116,118, 120, 122, 124, 156, 158, 160, 162, and 168 are illustrated asmetal-oxide-semiconductor field-effect transistors (MOSFETs). Otherswitches, such as bipolar junction transistors (BJTs), relay switches,etc., may be used instead of MOSFETs for the switches 92, 94, 96, 98,100, 116, 118, 120, 122, 124, 156, 158, 160, 162, and 168.

FIG. 10 illustrates a circuit 188 in which a switch 192 is mounted onthe outside of the tool 44 or the battery pack 40 to switch the circuit188 between the parallel and series configurations.

A transistor circuit may be used to switch the cells 12 between theparallel and series configurations. FIG. 11 illustrates an exampletransistor circuit 196 in a parallel configuration with two transistorsfor each path. As illustrated, the idle state of the circuit 196 haszero volts over the load resistance 200 and almost the whole batteryvoltage over one transistor in each path. As soon as the circuit getsswitched (all transistors switch together), the voltage drop over alltransistors equals zero. Furthermore, the battery voltages are changingand converge closer together. In addition to that, the load resistance200 shows a voltage drop with 20.6V. As a result, the battery pack 40 isconnected in a parallel configuration.

FIG. 12 illustrates the transistor circuit 196 with the battery pack 40in a series configuration. As illustrated, the idle state the circuit196 shows no voltage drop over the load resistance 20 and a voltage dropof 41.17V over a transistor 204 in the middle, meaning that thetransistor 204 is not switched in the idle state. As soon as thetransistor 204 (and with it the circuit) is switched, the voltage dropover the transistor 204 goes to zero, and the voltage drop over theresistor 200 changes from zero to 41.17V.

The transistor circuit 196 of FIGS. 11-12 is also illustrated in FIG. 13. FIG. 14 shows a printed circuit board implementation of the circuit196.

In some embodiments of the battery pack 40, the battery cells 12 may bemonitored by one or more monitoring integrated circuits (ICs) to, forexample, protect and extend the life of the cells 12 and of the batterypack 40. The cells 12 may be monitored to, for example, prevent orinhibit overvoltage, undervoltage, overcurrent in discharge, imbalance,etc. of the cells 12.

When a complete block 20 of cells 12 is monitored by connecting amonitoring device between the most positive terminal and the mostnegative terminal of the block 20, a total voltage of the block 20 ismonitored but not the individual cells 12. In such embodiments, themonitoring device may detect a reasonable value for the voltage of theblock 20 but may not detect undesirable conditions of the cells 12(e.g., cell imbalances) within the block 20. Hence, monitoring ICscapable of monitoring individual cells in a block 20 may beadvantageous.

Individual cell monitoring may be implemented to balance the cellsduring charging and discharging. For example, during charging, one cell12 may reach a threshold of approximately 4.2V before others cells 12,the monitoring IC may cut off charging of that cell 12, but charging ofother cells 12 will continue, for example, with a slightly highercurrent to reach the same threshold.

FIG. 24 illustrates a monitoring IC 220 of the battery pack 40 connectedto the battery cells 12. As illustrated, the monitoring IC 220 does notmonitor each cell 12 individually because connections to the individualcells 12 are missing. While the monitoring IC 220 may monitor the cells12 collectively from positive to negative, it is not be capable ofmonitoring individual cells 220.

The battery cells 12 may provide a supply voltage to the monitoring IC220. Accordingly, the monitoring IC 220 may need to be connected to thebattery blocks 8 or 20. When the battery pack 40 switchesconfigurations, the supply voltage for the monitoring IC 220 will alsoswitch between a low voltage level and a high voltage level. Exemplarydesigns are provided below to allow for monitoring cells individuallyand to handle the switching power supply voltage.

FIG. 25 illustrates an exemplary battery monitoring circuit 224 in aparallel configuration. In the illustrated embodiment, the batterymonitoring circuit 224 includes two separate monitoring ICs 228 and 232communicating with an electronic processor 234. In some embodiments, twomonitoring ICs 228 and 232 may be implemented using host-controlledanalog front ends (AFEs) capable of monitoring up to six or up to tencells connected in series.

The monitoring IC 228 may be used to monitor all ten cells 12 in aseries configuration while the monitoring IC 232 may be disconnectedfrom the cells 12, so that the monitoring IC 232 is not turned ON by thecell voltages. Furthermore, both monitoring ICs 228 and 232 may beconnected to the negative pole of the last cell 12 (for example, cell10), since this point serves as the star ground for the setup.

FIG. 26 illustrates the battery monitoring circuit 224 in a seriesconfiguration. In this configuration, the monitoring IC 232 may beunused, as it may only be used to monitor cells 12 in a parallel setup.Further, the monitoring ICs 228 and 232 may be designed to operate withfluctuating supply voltages to handle changing voltage levels resultingfrom switching between the parallel and series configurations.

FIG. 27 illustrates another exemplary battery monitoring circuit 236 ina series configuration. The battery monitoring circuit 236 is similar tothe battery monitoring circuit 224 of FIG. 25 , but two monitoring ICs240 and 244 monitor five cells 12 each. The monitoring IC 240 isconnected from Cell 10 through Cell 6, and the monitoring IC 244 isconnected from Cell 5 through Cell 1. Due to this connection, themonitoring IC 244 is connected between +36V and +18V whereas themonitoring IC 240 is connected between +18V and 0V such that bothmonitoring ICs 240 and 244 receive similar operating voltages. Bothmonitoring ICs 240 and 244 are connected to an electronic processor 248,which may be used to synchronize the monitoring ICs 240 and 244.

FIG. 28 illustrates the battery monitoring circuit 236 in a parallelconfiguration. As illustrated, both monitoring ICs 240 and 244 areconnected between +18V and 0V, and, therefore, no additional changes arerequired to the operating voltages of the monitoring ICs 240 and 244when the battery pack 40 switches between the parallel and seriesconfigurations.

In other embodiments, rather than multiple monitoring ICs each connectedto one block 20 of cells 12, a single monitoring IC may monitor a block20 of battery cells 12 for a short time and then jump to monitor asecond block 20 for a similar time period. Particularly, in the case ofcharging, voltage changes in the pack 40 may be very slow since acharger may use a very low current (6 amps) in comparison to possibledischarges through devices (30 amps and more). For example, the singlemonitoring IC may be used to monitor a first block 20 of battery cells12 for first period of time (e.g., 10 ms) and then to monitor a secondblock 20 of battery cells 12 for a second period of time (e.g., 10 ms)and so on.

FIG. 30 illustrates yet another exemplary battery monitoring circuit248. As illustrated, the battery monitoring circuit 248 includes two5S1P cell blocks 20A and 20B. The cell block 20A is monitored by anelectronic processor 252A using an analog front end (AFE) 256A. The cellblock 20B is monitored by an electronic processor 252B using an AFE256B.

The AFEs 256A-B are capable of monitoring individual cells in the cellblocks 20A-B. The AFEs 256A-B may be implemented using, for example,BQ76925 host-controlled analog front end designed by Texas Instruments.The AFEs 256A-B may be referred to singularly as the AFE 256, and theprocessors 252A-B may be referred to singularly as the processor 252. Inother embodiments, the battery monitoring circuit 248 may include moreor fewer cell blocks 20 monitored by more or fewer processors 252 andAFEs 256.

The AFE 256 provides operating power to the processor 252 over the V3P3line. The processor 252 provides serial clock (SCL) to the AFE 256 overthe SCL line. The processor 252 and the AFE 256 exchange serial dataover the SDA line. For example, the processor 252 may write an addressof an individual cell to be monitored at a given time to a register ofthe AFE 256 over the SDA line. The AFE 256 provides a reference voltageused to measure individual voltages of the battery cells 12 over theVREF+ line to the processor 252. The AFE 256 provides individual states(for example, voltages of individual cells 12) over the VCOUT line tothe processor 252. The AFE 256 may provide a voltage of a particularcell 12 at the VCOUT line based on request written to the AFE 256 overthe SDA line. The battery monitoring circuit 248 may additionallyinclude a coupling circuit, for example, an opto-coupling circuit 258that facilitates communication between the processors 252A-B and anelectronic processor of a tool.

FIG. 31 illustrates a further alternative battery monitoring circuit260. As illustrated, the battery monitoring circuit 260 includes three5S1P cell blocks 20A-C. Each cell block 20A-C is monitored by a singleelectronic processor 264 using AFEs 268A-C, respectively. As describedabove, the AFEs 268A-C are capable of monitoring individual cells 12 inthe cell blocks 20A-C. The AFEs 268A-C may be referred to singularly asthe AFE 268. In other embodiments, the battery monitoring circuit 248may include more or fewer cell blocks 20 monitored by the processor 264using more or fewer AFEs 268.

The processor 264 may receive operating power from one of the AFEs 268.The processor 264 provides a serial clock over the SCL lines to the AFEs268A-C. In addition, the processor 264 and the AFEs 268A-C exchangeserial data over the SDA lines. The processor 264 may receive referencevoltages (VREF+) and individual cell states (VCOUT) at analog inputsANI0-5. In the illustrated example, analog inputs ANI0-1 are connectedto AFE 268A, analog inputs ANI2-3 are connected to AFE 268B, and analoginputs ANI4-5 are connected to AFE 268C.

FIG. 32 illustrates another alternative battery monitoring circuit 272using shared inter-integrated circuit (I2C) bus. As illustrated, thebattery monitoring circuit 272 includes three 5S1P cell blocks 20A-Cmonitored by a single electronic processor 276 using AFEs 280A-C,respectively. The battery monitoring circuit 272 operates in a similarmanner to the battery monitoring circuit 260 of FIG. 31 .

The AFEs 280A-C communicate with the processor 276 over a shared I2Cchannel. Outputs of the AFEs 280A-C are provided at analog inputs ANI0-3of the processor 276. Because all cells 12 in the cell blocks 20A-Coperate at similar voltage levels, the processor 276 may be providedwith a single reference voltage (VREF+) from the AFE 280A. The referencevoltage VREF+ is provided at the analog input ANI0. States of individualcells (VCOUT) are provided at analog inputs ANI1-3 from the AFEs 280A-C,respectively. The battery monitoring circuit 272 may include more orfewer cell blocks 20 monitored by the processor 276 using more of fewerAFEs 280 over the shared I2C channel. The battery monitoring circuit 272may also include an opto-coupling circuit 284.

FIGS. 33A-B illustrate yet another alternative battery monitoringcircuit 288 using multiplexors. As illustrated, the battery monitoringcircuit 288 includes four 5S1P cell blocks 20A-D monitored by a singleelectronic processor 292 using AFEs 296A-D. The battery monitoringcircuit 288 operates in a manner similar to the battery monitoringcircuit 272 of FIG. 32 .

The AFEs 296A-D communicate with the processor 292 over a shared I2Cchannel. As shown in FIG. 33A, a multiplexor 300 is connected betweenthe processor 292 and the AFEs 296A-D on the shared I2C channel. Theprocessor 292 provides selection inputs to the multiplexor 300 in orderto select an AFE 296 between the 296A-D with which the processor 292exchanges communications at a particular time. As shown in FIG. 33B,multiple multiplexors 300A-B may also be used over multiple I2C channelsto facilitate communications between the processor 292 and the AFEs296A-D. The battery monitoring circuit 288 may also include anopto-coupling circuit 302.

FIG. 34 illustrates a further alternative battery monitoring circuit 304using multiple inter-integrated circuit (I2C) buses. As illustrated, thebattery monitoring circuit 304 includes three 5S1P cell blocks 20A-Cmonitored by a single electronic processor 308 using AFEs 312A-Crespectively. The battery monitoring circuit 304 operates in a mannersimilar to the battery monitoring circuit 272 of FIG. 32 . However, theAFEs 312A-C communicate with the processor 308 over multiple I2Cchannels.

For example, the AFE 312A communicates with the processor 308 over I2Cchannel I2C 1, the AFE 312B communicates with the processor 308 over I2Cchannel I2C 2, and so on. Outputs of the AFEs 312A-C are provided atanalog inputs ANI0-3 of the processor 304 similar to the batterymonitoring circuit 272 of FIG. 32 . The battery monitoring circuit 304may include more or fewer cell blocks 20 monitored by the processor 308using more or fewer AFEs 312 over multiple I2C channels. The batterymonitoring circuit 304 may also include an opto-coupling circuit 316.

FIG. 35 illustrates another alternative battery monitoring circuit 320using serial peripheral interface. As illustrated, several 5S1P block 20are monitored by a single electronic processor 324 using several AFEs328. The AFEs 328 communicate with the processor 324 using serialperipheral interface bus. The battery monitoring circuit 320 may alsoinclude several switches 332 with resistors connected across each cellblock 20 to discharge the cell blocks 20 during cell balancing.

As mentioned above, the low-voltage tool and the high-voltage tool maybe different tools, each operating at the given voltage level. As alsomentioned above, the low-voltage tool and the high-voltage tool may beone tool (or other electrical device) capable of operating in differentvoltage levels or modes.

For example, the dual-mode battery pack 40 may be used to power a toolhaving a reconfigurable, dual-mode motor operable to run under differentvoltage levels. For instance, the tool may have a low voltage level mode(e.g., an 18V mode; with an increased amp-hour capacity or run-time) inwhich the motor is configured to be optimally powered by a low voltagepower source, and a high voltage level mode (e.g., a 36V mode) in whichthe motor is configured to be optimally powered by a high voltage powersource. Setting the tool and battery pack 40 to an optimal voltage levelcan, in turn, lead to a more efficient motor operation at the givenvoltage level.

As another example, the dual-mode tool may be another electrical devicehaving a reconfigurable, dual-mode load.

As described above, the invention may generally provide, among otherthings, a dual-mode battery pack and methods and systems to implementthe dual-mode arrangement. The invention may also generally providemethods and systems for monitoring and/or balancing individual cells.

One or more independent features and/or independent advantages of theinvention may be set forth in the following claims:

What is claimed is:
 1. A battery pack comprising: a housing; a first setof battery cells connected in series and positioned in the housing; asecond set of battery cells connected in series and positioned in thehousing; a first analog front end connected to the first set of batterycells and configured to individually monitor each cell of the first setof battery cells; a second analog front end connected to the second setof battery cells and configured to individually monitor each cell of thesecond set of battery cells; an electronic processor connected to thefirst analog front end and the second analog front end; and amultiplexor coupled between (i) the electronic processor and (ii) thefirst analog front end and the second analog front end, wherein theelectronic processor is configured to provide a selection signal to themultiplexor to select between the first analog front end and the secondanalog front end for communication with the electronic processor.
 2. Thebattery pack of claim 1, wherein the first set of battery cells includesa first plurality of battery cells and wherein the first analog frontend is configured to individually monitor a voltage of each of the firstplurality of battery cells.
 3. The battery pack of claim 2, wherein theelectronic processor is configured to: receive a plurality of voltagevalues for the first plurality of battery cells from the first analogfront end, and balance the first plurality of battery cells based on theplurality of the voltage values.
 4. The battery pack of claim 2, whereinthe second set of battery cells includes a second plurality of batterycells and wherein the second analog front end is configured toindividually monitor a voltage of each of the second plurality ofbattery cells.
 5. The battery pack of claim 4, wherein the processor isconfigured to: receive a second plurality of voltage values for thesecond plurality of battery cells from the second analog front end; andbalance the second plurality of battery cells based on the secondplurality of the voltage values.
 6. The battery pack of claim 1, whereinthe multiplexor is a first multiplexor and the selection signal is afirst selection signal, further comprising: a third set of battery cellsconnected in series and positioned in the housing; a fourth set ofbattery cells connected in series and positioned in the housing; a thirdanalog front end connected to the third set of battery cells andconfigured to individually monitor each cell of the third set of batterycells; a fourth analog front end connected to the fourth set of batterycells and configured to individually monitor each cell of the fourth setof battery cells; a second multiplexor coupled between (i) theelectronic processor and (ii) the third analog front end and the fourthanalog front end, wherein the electronic processor is configured toprovide a second selection signal to the second multiplexor to selectbetween the third analog front end and the fourth analog front end forcommunication with the electronic processor.
 7. The battery pack ofclaim 6, further comprising a plurality of inter-integrated circuitchannels for connection between the electronic processor, the firstmultiplexor, the second multiplexor, the first analog front end, thesecond analog front end, the third analog front end, and the fourthanalog front end.
 8. The battery pack of claim 1, further comprising:series connection contacts configured to connect the first set ofbattery cells and the second set of battery cells in series when theseries connection contacts are closed; and parallel connection contactsconfigured to connect the first set of battery cells and the second setof battery cells in parallel when the parallel connection contacts areclosed, wherein one of the series connection contacts and the parallelconnection contacts are closed when engaged by one or more conductiveblades of an external electronic device, wherein the other of the seriesconnection contacts and the parallel connection contacts are opened whenengaged by one or more insulating ribs of the external electronicdevice.
 9. A method for monitoring a battery pack comprising: connectinga first set of battery cells in series; connecting a second set ofbattery cells in series; individually monitoring, using a first analogfront end, each cell of the first set of battery cells; individuallymonitoring, using a second analog front end, each cell of the second setof battery cells; synchronizing, using an electronic processor,monitoring by the first analog front end and the second analog frontend; and providing, using the electronic processor, a selection signalto a multiplexor connected between (i) the electronic processor and (ii)the first analog front end and the second analog front end to selectbetween the first analog front end and the second analog front end forcommunication with the electronic processor.
 10. The method of claim 9,wherein the first set of battery cells includes a first plurality ofbattery cells and wherein individually monitoring each cell of the firstset of battery cells further comprises individually monitoring a voltageof each of the first plurality of battery cells.
 11. The method of claim10, further comprising: receiving, at the electronic processor, aplurality of voltage values for the first plurality of battery cellsfrom the first analog front end, and balancing, using the electronicprocessor, the first plurality of battery cells based on the pluralityof the voltage values.
 12. The method of claim 9, wherein the second setof battery cells includes a second plurality of battery cells andwherein individually monitoring each cell of the second plurality ofbattery cells further comprises individually monitoring a voltage ofeach of the second plurality of battery cells.
 13. The method of claim12, further comprising: receiving, at the electronic processor, a secondplurality of voltage values for the second plurality of battery cellsfrom the second analog front end, and balancing, using the electronicprocessor, the second plurality of battery cells based on the secondplurality of the voltage values.
 14. The method of claim 9, wherein themultiplexor is a first multiplexor and the selection signal is a firstselection signal, further comprising: connecting a third set of batterycells in series; connecting a fourth set of battery cells in series;individually monitoring, using a third analog front end, each cell ofthe third set of battery cells; individually monitoring, using a secondanalog front end, each cell of the fourth set of battery cells;synchronizing, using an electronic processor, monitoring by the thirdanalog front end and the fourth analog front end; and providing, usingthe electronic processor, a second selection signal to a secondmultiplexor connected between (i) the electronic processor and (ii) thethird analog front end and the fourth analog front end to select betweenthe third analog front end and the fourth analog front end forcommunication with the electronic processor.
 15. The method of claim 9,further comprising: disengaging, with an insulating rib of a power tool,parallel connection contacts operable to connect the first set ofbattery cells and the second set of battery cells in parallel, the powertool being external to the battery pack; and engaging, with conductingblades of the power tool, series connection contacts to connect thefirst set of battery cells and the second set of battery cells inseries, wherein disengaging the parallel connection contacts occursbefore engaging the series connection contacts.
 16. The method of claim15, further comprising: disengaging the series connection contacts; andengaging the parallel connection contacts, wherein disengaging theseries connection contacts occurs before engaging the parallelconnection contacts.
 17. A battery pack comprising: a housing; a firstset of battery cells positioned in the housing; a second set of batterycells positioned in the housing; a third set of battery cells positionedin the housing; a fourth set of battery cells positioned in the housing;a first front end connected to the first set of battery cells andconfigured to individually monitor each cell of the first set of batterycells; a second front end connected to the second set of battery cellsand configured to individually monitor each cell of the second set ofbattery cells; a third front end connected to the third set of batterycells and configured to individually monitor each cell of the third setof battery cells; a fourth front end connected to the fourth set ofbattery cells and configured to individually monitor each cell of thefourth set of battery cells; an electronic processor connected to thefirst front end and the second front end; and a first multiplexorcoupled between (i) the electronic processor and (ii) the first frontend and the second front end, wherein the electronic processor isconfigured to provide a first selection signal to the multiplexor toselect between the first front end and the second front end forcommunication with the electronic processor a second multiplexor coupledbetween (i) the electronic processor and (ii) the third front end andthe fourth front end, wherein the electronic processor is configured toprovide a second selection signal to the second multiplexor to selectbetween the third front end and the fourth front end for communicationwith the electronic processor.
 18. The battery pack of claim 17, furthercomprising a plurality of inter-integrated circuit channels forconnection between the electronic processor, the first multiplexor, thesecond multiplexor, the first front end, the second front end, the thirdfront end, and the fourth front end.
 19. The battery pack of claim 17,wherein the electronic processor is configured to: receive a firstplurality of voltage values for the first plurality of battery cellsfrom the first front end through the first multiplexor; receive a secondplurality of voltage values for the second plurality of battery cellsfrom the second front end through the first multiplexor; and balance thefirst plurality of battery cells and the second plurality of batterycells based on the plurality of the voltage values.
 20. The battery packof claim 17, wherein the electronic processor is configured to: receivea third plurality of voltage values for the third plurality of batterycells from the third front end through the second multiplexor; receive afourth plurality of voltage values for the fourth plurality of batterycells from the fourth front end through the second multiplexor; andbalance the third plurality of battery cells and the fourth plurality ofbattery cells based on the plurality of the voltage values.